This invention relates to a magnetic recording medium, and more specifically to such a medium having a thin ferromagnetic metal film formed on the base characterized by a layer of a plasma-polymerized organic material sandwiched between the base and the ferromagnetic film.
Magnetic recording mediums of the type consisting of a substrate coated with a magnetic coating composition of a ferromagnetic powder and an organic binder have been extensively used. With those coated mediums, however, the presence of the binder renders it theoretically next to impossible to attain a greater residual magnetic flux density than the range of 3,000 to 4,000 gauss. Recently, qualitative improvements in and fast spreading market for magnetic recording mediums have created a steadily growing demand for those mediums capable of higher density recording of information than heretofore. To meet this requirement magnetic recording mediums of the thin ferromagnetic film type are under development. The thin metal film type medium is obtained by forming a thin film of a ferromagnetic metal, e.g., an iron family element or alloy, on a base by vacuum deposition, sputtering, ion plating, ion beam deposition, electrochemical deposition or the like. Of those techniques, vacuum deposition is deemed the most promising method for obtaining great lengths of film on an industrial scale, and much research is being made by many workers.
The magnetic recording medium is required to possess important properties, and the still characteristic in particular. If good still reproduction is to be ensured during the playback of the medium on a video tape recorder it is imperative to avoid the wear of the magnetic tape surface due to its contact with the reproducing heads. For example, with a VTR of a certain system, still reproduction is effected by scanning a given portion of the tape arcuately held along a rotating head by means of two magnetic heads attached 180.degree. apart to a fast rotating drum. If the tape has a low wear resistance, the scanning will gradually scrape out the tape surface to shorten the still duration. It is therefore important to minimize the tape wear on scanning by the magnetic heads running at a high speed and extend the reproduction time. This is particularly true with the narrow-track heads that have come into use to meet the requirement for high density recording but which badly shorten the still-sustaining time.
Efforts have been made to prolong the still duration of the coated type magnetic recording mediums by introducing varied abrasives into the coats on the tapes, and they have given favorable results.
On the other hand, the thin metal film type can scarcely be improved in the still characteristic for a number of reasons, including the difficulty of adding those abrasives and the thinness of the layer.
Attempts to improve the wear resistance of the thin metal film type by forming a special top coat on the magnetic layer have proved effective to some extent, but alternatives have been called for since the top coating invites other drawbacks.
As a result of a search for such an alternative, it has now been found that the still reproduction time can be extended by sandwiching a thin organic material layer, preferably an organometallic layer, formed by plasma polymerization between the base and the thin ferromagnetic metal layer. The present invention is predicated upon this discovery.